Method for dynamically adjusting resonant cavity frequency of cyclotron and tuning circuit

Abstract

The invention discloses a method for dynamically adjusting the frequency of a resonant cavity of a cyclotron and a tuning circuit, which are applied to the field of cyclotrons and solve the problem that when the frequency of the resonant cavity of the cyclotron is adjusted by judging the magnitude of reflection power, due to the fact that the reflection power can change in multiple stages in a single macro pulse period, the frequency of the resonant cavity of the cyclotron is adjusted. And an accurate numerical value is difficult to obtain through a simple amplitude sampling circuit. According to the invention, through determining the stable resonance time period of the resonant cavity, the phase difference between the incident power signal and the reflection power signal is sampled in the corresponding stable resonance time period of the resonant cavity, and the change value of the phase difference between the incident power signal and the reflection power signal is dynamically compared. According to the conversion relation between the phase difference change value and the frequency change value, the resonant cavity frequency change value is obtained through conversion, then the resonant cavity tuning device is adjusted to enable the resonant cavity frequency to be consistent with the frequency of the incident power signal all the time, and the dynamic tuning method of the resonant cavity is achieved.

Description

Technical Field

[0001] The invention relates to the field of cyclotron accelerators, and in particular to a method and a tuning circuit for dynamically adjusting the frequency of a cyclotron resonant cavity. Background Art

[0002] The resonant cavity of the cyclotron is a component used to generate the electric field required for ion acceleration. During the operation of the resonant cavity, the electromagnetic loss of the material may cause the cavity wall to heat up, or the structural shape of the resonant cavity may change due to the adjustment of the position of the internal ion source and other devices, which may cause the frequency of the resonant cavity to change, that is, the frequency has "drifted". When the frequency of the resonant cavity is inconsistent with the frequency of the incident power signal, it will cause the "total reflection" phenomenon, that is, the incident power signal will be completely reflected into the power amplifier, causing the power amplifier to work unstably and the accelerator resonant cavity to be unable to establish an accelerating electric field.

[0003] In order to solve the above problems, in the prior art, the length or position of the cavity tuning capacitor rod (plate), tuning probe and other devices in the resonant cavity is usually adjusted according to the size of the reflected power to adjust the frequency of the resonant cavity so that it is always consistent with the frequency of the incident power signal. For example, after an accelerator has been running at full power in the resonant cavity for 20 minutes, it is determined that the reflected power of the cavity exceeds a reasonable range, and the tuning capacitor plate in the resonant cavity is deflected by 3° to offset the frequency drift caused by the heating of the resonant cavity. After multiple adjustments are made until the resonant cavity reaches thermal equilibrium (no more thermal deformation), the adjustment action can be stopped.

[0004] However, the judgment on the adjustment action of the cavity tuning capacitor rod (plate), tuning probe and other devices is based on the reflected power. The reflected power will change in multiple stages within a single macro pulse cycle, and it is difficult to obtain accurate values ​​through a simple amplitude sampling circuit. Different devices of the same model need to be tested repeatedly to obtain more accurate operating experience. In addition, this adjustment method is not suitable for the continuous wave state. The effective power in the continuous wave state is higher than that in the macro pulse state. The state of the cavity changes rapidly. The same operation cannot be used to compensate for the frequency drift of the resonant cavity. There is a risk of burning out devices such as couplers due to untimely adjustment.

[0005] In addition, even if some technical means are adopted to realize compensation for the resonant cavity frequency drift by monitoring the reflected power, the means commonly used in the prior art is to frequently and dynamically adjust the signal frequency of the power source so that the incident power signal frequency of the power source is consistent with the changed resonant cavity frequency. However, in the field of cyclotron accelerators, the cyclotron period of particles is determined by the magnetic field of the accelerator. Frequent and dynamic adjustment of the signal frequency of the power source will cause the signal frequency of the power source and the changed resonant cavity frequency to be mismatched with the magnetic field of the accelerator, which will cause the cyclotron frequency of the particles to be inconsistent with the frequency of change of the radio frequency electric field, making it difficult for the particles to accelerate at the ideal time, and thus causing the capture phase width of the central area of ​​the accelerator, the single-turn energy gain of the accelerator and other indicators to deviate from the design values, and ultimately it is difficult to obtain a high-intensity, high-quality beam; part of the beam will also cause the beam to "slip" because the cyclotron frequency of the particles is inconsistent with the frequency of change of the radio frequency electric field, and the orbit of the bunch will deviate from the design value and bombard the vacuum box and other devices, causing the activation level of the accelerator to rise, making the operation and maintenance of the accelerator difficult.

[0006] Therefore, it is necessary to improve the situation where the frequency drift of the cyclotron's resonant cavity occurs during operation without changing the power source signal frequency, so as to dynamically adjust the cyclotron's resonant cavity frequency and make the resonant cavity frequency always consistent with the power source signal frequency, and at the same time match the accelerator's magnetic field to ensure the stable operation of the cyclotron accelerator and obtain a high-intensity, high-quality beam. Summary of the invention

[0007] The present invention aims to provide a method and a tuning circuit for dynamically adjusting the resonant cavity frequency of a cyclotron, so as to solve the technical problem in the prior art that when adjusting the resonant cavity frequency of a cyclotron by judging the magnitude of reflected power, it is difficult to obtain accurate numerical values ​​through a simple amplitude sampling circuit because the reflected power will change in multiple stages within a single macro pulse cycle. In actual operation, it is necessary to conduct repeated tests many times to obtain more accurate operating experience, resulting in low operating efficiency, poor adjustment effect, and high time cost. Based on the above problems, the present invention proposes a method for analyzing the change of the waveform of the incident power signal with the response time to determine the time period of stable resonance of the resonant cavity, sampling the phase difference between the incident power signal and the reflected power signal in the corresponding time period of stable resonance of the resonant cavity, dynamically comparing the phase difference between the incident power signal and the reflected power signal, and converting the resonant cavity frequency change value according to the conversion relationship between the phase difference change value and the frequency change value, and then adjusting the resonant cavity tuning device so that the resonant cavity frequency is always consistent with the frequency of the incident power signal to achieve dynamic tuning of the resonant cavity, and based on this method, a specific circuit design is given, which can compensate for the changes in the resonant cavity frequency caused by multiple reasons under multiple working conditions, and realize the ability to dynamically adjust the resonant cavity frequency of the cyclotron accelerator, so that the resonant cavity frequency is always consistent with the power source signal frequency, and at the same time matches the magnetic field of the accelerator, thereby ensuring stable operation of the cyclotron accelerator and obtaining a high-intensity, high-quality beam.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] In a first aspect, based on the technical problem solved above, the present invention provides a method for dynamically adjusting the frequency of a cyclotron resonant cavity, comprising the following steps:

[0010] S1, obtaining a first time length, wherein the first time length is greater than or equal to the time length required for the resonant cavity to reach a resonant state from an initial state;

[0011] S2, feeding an incident power signal into the resonant cavity, wherein the incident power signal matches the particle acceleration parameter in the cyclotron, and the time when the resonant cavity starts to receive the incident power signal is recorded as the initial time;

[0012] S3, according to the first duration, taking the end time of the first duration as the sampling time, and sampling the incident power signal and the reflected power signal at the same time at the sampling time;

[0013] S4, preset the target range of the resonant cavity frequency change;

[0014] S5, analyzing the sampled incident power signal and reflected power signal and converting them to obtain the resonant cavity frequency change value Δf; and determining whether the resonant cavity frequency change value Δf is within the resonant cavity frequency change target range preset in step S4;

[0015] If the resonant cavity frequency change value Δf is within the preset resonant cavity frequency change target range, then continue to repeat steps S2 to S5;

[0016] If the resonant cavity frequency change value Δf is outside the preset resonant cavity frequency change target range, the process jumps to step S6;

[0017] S6. Adjust the resonant cavity frequency according to the resonant cavity frequency change value Δf, and return to execute steps S1 to S5 to achieve dynamic adjustment of the cyclotron resonant cavity frequency.

[0018] Preferably, in step S1, obtaining the first duration includes the following steps:

[0019] S1.1, feeding an incident power signal into the resonant cavity, wherein the incident power signal matches the particle acceleration parameter in the cyclotron, and the time when the resonant cavity starts to receive the incident power signal is recorded as the initial time;

[0020] S1.2, performing waveform detection on the reflected power signal of the resonant cavity;

[0021] S1.3, according to the reflected power signal waveform of the resonant cavity, the moment when the reflected power signal waveform enters a stable state is taken as the moment when the resonant cavity enters a resonant state;

[0022] S1.4. Subtract the time when the resonant cavity enters the resonant state from the initial time to obtain the first duration.

[0023] Preferably, in step S2, the incident power signal is obtained by amplifying the power of a signal source outputting a signal with a frequency of f1; the frequency f1 matches the particle acceleration parameter in the cyclotron; wherein f1=f0, f0 is the static frequency of the resonant cavity;

[0024] The signal with the frequency f1 is a pulse signal or a continuous signal.

[0025] Preferably, the signal with a frequency of f1 is a pulse signal, and correspondingly, the resonant cavity has a first moment t1, a second moment t2 and a third moment t3 in each pulse cycle; at the second moment t2, the resonant cavity reaches a resonant state, and at the third moment t3, the resonant cavity enters an oscillating state; the first time length is set to be greater than or equal to t2-t1 and less than or equal to t3-t2;

[0026] In step S5, the sampled incident power signal and reflected power signal are analyzed and converted to obtain a resonant cavity frequency change value, including the following steps:

[0027] S5.1. At a sampling time corresponding to the first pulse signal, the phases of the incident power signal and the reflected power signal are respectively collected, and a first phase difference ΔPhase0 is obtained;

[0028] S5.2, at a sampling time corresponding to a second pulse signal, respectively collecting the phases of the incident power signal and the reflected power signal, and obtaining a second phase difference ΔPhase′; the second pulse signal is the next pulse signal adjacent to the first pulse signal;

[0029] S5.3, according to the first phase difference ΔPhase0 and the second phase difference ΔPhase′ obtained in steps S5.2 and S5.3, calculate the phase difference change value delta=ΔPhase′-ΔPhase0;

[0030] S5.4. According to the phase difference change value delta obtained in step S5.3, the corresponding resonant cavity frequency change value Δf is converted.

[0031] Preferably, in step S6, the frequency of the resonant cavity is adjusted by using a tuning rod extending into the resonant cavity; before executing step S6, the relationship between the length change value ΔL of the tuning rod extending into the resonant cavity and the resonant cavity frequency change Δf is first obtained. In step S6, according to the resonant cavity frequency change value Δf, the corresponding length change value ΔL of the tuning rod extending into the resonant cavity is obtained, and then the length of the tuning rod extending into the resonant cavity is adjusted to adjust the resonant cavity frequency.

[0032] Preferably, in step S2, the signal source is a radio frequency signal source, the signal with a frequency of f1 is a macro-pulse modulated signal after macro-pulse modulation, and the macro-pulse modulated signal switches between a low level state and a high level state; when executing step S5, the macro-pulse modulated signal is in a high level state.

[0033] Preferably, in step S2, the signal source is a radio frequency signal source, the signal with a frequency of f1 is a continuous wave signal, and while the signal source outputs the continuous wave signal, the signal source is also set to generate a trigger signal according to a preset period, and the initial signal of the trigger signal is the moment when the first duration ends.

[0034] In a second aspect, the present invention further provides a tuning circuit for dynamically adjusting the frequency of a cyclotron resonant cavity, which is used to implement the method for dynamically adjusting the frequency of a cyclotron resonant cavity as described above, comprising:

[0035] A signal source, used for outputting a pulse signal with a frequency of f1;

[0036] A power amplifier is used to amplify the signal with a frequency of f1 output by the signal source to obtain an incident power signal;

[0037] An amplitude and phase detection circuit, used for receiving an incident power signal and a reflected power signal respectively, and outputting a phase difference between the incident power signal and the reflected power signal;

[0038] The sampler and holder is used to sample and hold the phase difference output by the amplitude and phase detection circuit at a non-sampling time, and the signal output end of the amplitude and phase detection circuit is connected to the signal input end of the sampler and holder.

[0039] This circuit obtains the phase difference between the incident power signal (hereinafter referred to as the Pin signal) and the reflected power signal (hereinafter referred to as the Pick-up signal) through the amplitude and phase detection circuits, and according to the above-mentioned method for dynamically adjusting the cyclotron accelerator resonant cavity frequency, the resonant cavity frequency change value is converted according to the conversion relationship between the phase difference change value and the frequency change value, and then the cyclotron resonant cavity frequency drift is compensated, ensuring that the cyclotron accelerator can always maintain a stable working state under conditions such as changes in the resonant cavity caused by temperature and adjustment of the ion source position.

[0040] Preferably, the tuning circuit also includes a first bandpass filter and a second bandpass filter; the functional parameters of the first bandpass filter and the second bandpass filter are the same; the first bandpass filter is used to receive the incident power signal output from the directional coupler; the second bandpass filter is used to receive the reflected power signal from the resonant cavity; the signal output ends of the first bandpass filter and the second bandpass filter are simultaneously connected to the signal input ends of the amplitude and phase detection circuit.

[0041] The two inputs of the amplitude detection and phase detection circuit are respectively derived from the incident power signal output by the directional coupler and the reflected power signal of the resonant cavity, and the two signals are filtered by the same bandpass filter before being input into the amplitude detection and phase detection circuit; on the one hand, the second bandpass filter can filter out the spurious signals generated by the secondary electrons or other factors in the Pick-up signal, so that the amplitude detection and phase detection circuit can work stably; on the other hand, since the second bandpass filter itself will produce a phase delay on the input signal, and the phase delay effect on signals of different frequencies in the working frequency band is different, the first bandpass filter is added, and the functional parameters of the two bandpass filters are made the same, which can eliminate the phase delay error caused by a single filter when the cyclotron works at different frequencies (considering that the signal source frequency is consistent with the cyclotron frequency).

[0042] As one implementation method of calculating the phase difference change value, the tuning circuit further includes an ADC circuit and a PLC; the signal input end of the ADC circuit is connected to the signal output end of the sample holder, and the signal output end of the ADC circuit is connected to the signal input end of the PLC; the signal output end of the PLC is used to connect to the tuning device;

[0043] The ADC circuit is used to receive the phase difference signal output by the amplitude and phase detection circuit, and convert it into a digital signal and send it to the PLC for storage;

[0044] The PLC is used to store and calculate the phase difference change value within the same preset interval time, and convert it to obtain the corresponding resonant cavity frequency change value, and control the tuning device to perform frequency adjustment action according to the resonant cavity frequency change value.

[0045] The present invention has the following beneficial effects:

[0046] The present invention can be applied to the field of cyclotron accelerators, and specifically relates to the dynamic adjustment of the resonant cavity frequency of the cyclotron accelerator, and solves the technical problem in the prior art that when the resonant cavity frequency of the cyclotron accelerator is adjusted by judging the magnitude of the reflected power, it is difficult to obtain an accurate numerical value through a simple amplitude sampling circuit because the reflected power will change in multiple stages within a single macro pulse cycle; the present invention determines the time period of stable resonance of the resonant cavity, samples the phase difference between the incident power signal and the reflected power signal in the corresponding time period of stable resonance of the resonant cavity, and dynamically compares the phase difference change value between the incident power signal and the reflected power signal, and converts the resonant cavity frequency change value according to the conversion relationship between the phase difference change value and the frequency change value, and then adjusts the resonant cavity tuning device so that the resonant cavity frequency is always consistent with the frequency of the incident power signal, and realizes the method of dynamic tuning of the resonant cavity, so as to realize the method of being able to dynamically adjust the resonant cavity frequency of the cyclotron accelerator, and make the resonant cavity frequency always consistent with the power source signal frequency, and at the same time match the magnetic field of the accelerator, so as to ensure the stable operation of the cyclotron accelerator and obtain a high-intensity and high-quality beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0048] Figure 1 Schematic diagram of a tuning circuit for dynamically adjusting the cyclotron cavity frequency according to an embodiment of the present invention.

[0049] Figure 2 1 is a comparison diagram of signal waveforms output by various components in the tuning circuit of an embodiment of the present invention.

[0050] Explanation of the reference numerals: 100, resonant cavity; 200, tuning device; 300, tuning circuit; 301, signal source; 302, power amplifier; 303, directional coupler; 304, first band-pass filter; 305, second band-pass filter; 306, amplitude and phase detection circuit; 307, sample and hold; 308, ADC circuit; 309, comparator; 310, PLC. DETAILED DESCRIPTION

[0051] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0052] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] The present invention can be applied to the field of cyclotrons, and specifically relates to the dynamic adjustment of the resonant cavity frequency of the cyclotron, and solves the technical problem in the prior art that when the resonant cavity frequency of the cyclotron is adjusted by judging the size of the reflected power, it is difficult to obtain an accurate numerical value through a simple amplitude sampling circuit because the reflected power will change in multiple stages within a single macro pulse cycle. Even different devices of the same model need to be tested repeatedly for many times to obtain more accurate operating experience, which requires operators to continuously perform repeated tests. The operators have different levels of skills and the operation is highly complicated, which results in low operating efficiency, poor adjustment effect and high time cost.

[0054] The present invention proposes a method for dynamically comparing the phase difference between the incident power signal and the reflected power signal, and converting the resonant cavity frequency change value according to the conversion relationship between the phase difference change value and the frequency change value, and then adjusting the resonant cavity tuning device so that the resonant cavity frequency is always consistent with the frequency of the incident power signal to achieve dynamic tuning of the resonant cavity, and based on this method, a specific circuit design is given, which can compensate for the resonant cavity frequency changes caused by multiple working conditions and multiple reasons, so that the resonant cavity frequency is always consistent with the preset frequency, and the cyclotron resonant cavity and power amplifier are guaranteed to work stably. Among them, the phase difference between the incident power signal and the reflected power signal is dynamically compared, and the resonant cavity frequency change value is converted according to the conversion relationship between the phase difference change value and the frequency change value. The core idea is that there is a positive correlation between the frequency difference and the phase difference, and the change in the resonant cavity frequency can be inferred from the value of the phase difference change. According to the change, the corresponding action can be taken to return the signal source to the resonant state.

[0055] During the operation of the cyclotron accelerator, the frequency of the resonant cavity changes for the following reasons: After the resonant cavity has been operating for a period of time, since the resonant cavity material is not an ideal electrical conductor, heat will be generated in various parts of the resonant cavity due to resistance loss. After the material is heated, thermal deformation will occur, causing the resonant cavity frequency to change from f0 to f2. The resonant cavity frequency is no longer equal to the signal source frequency, that is, f2≠f0. The incident power will be reflected to the power amplifier, causing the power amplifier to work unstable. At the same time, the actual power entering the resonant cavity (actual power = incident power - reflected power) is reduced, and the electric field that meets the particle acceleration cannot be established in the resonant cavity or the electric field amplitude seriously deviates from the design value, making the accelerator unstable.

[0056] In addition, during the operation of the internal ion source cyclotron accelerator, the position of the ion source in the accelerator needs to be adjusted according to the beam intensity obtained outside the central area. Such adjustments will also cause changes in the capacitance distribution inside the resonant cavity, thereby changing the frequency of the resonant cavity.

[0057] Example 1, please refer to Figure 1Based on the above-mentioned technical problems and the method for dynamically adjusting the frequency of a cyclotron resonant cavity, this embodiment provides a tuning circuit for dynamically adjusting the frequency of a cyclotron resonant cavity, including:

[0058] A signal source 301, used for outputting a signal with a frequency of f1;

[0059] The power amplifier 302 is used to amplify the signal with a frequency of f1 output by the signal source 301 to obtain an incident power signal;

[0060] The incident power signal amplitude and phase detection circuit 306 is used to receive the incident power signal output from the directional coupler 303 and the resonant cavity 100 reflected power signal from the resonant cavity 100, and output the phase difference between the incident power signal and the resonant cavity 100 reflected power signal;

[0061] The sample and hold device 307 is used to sample and hold the phase difference output by the amplitude and phase detection circuit at a non-sampling time. The signal output end of the amplitude and phase detection circuit 306 is connected to the signal input end of the sample and hold device 307 .

[0062] This circuit obtains the phase difference between the incident power signal (hereinafter referred to as the Pin signal) and the reflected power signal (hereinafter referred to as the Pick-up signal) through the amplitude and phase detection circuit 306. According to the above-mentioned method for dynamically adjusting the frequency of the cyclotron resonant cavity 100, the change value of the frequency of the resonant cavity 100 is converted according to the conversion relationship between the phase difference change value and the frequency change value, and then the frequency drift of the cyclotron resonant cavity 100 is compensated, ensuring that the cyclotron can always maintain a stable working state under conditions such as changes in the resonant cavity 100 caused by temperature and adjustment of the ion source position. Specifically, the Pick-up signal can be given in the form of capacitive coupling or inductive coupling, and the setting position can be located in multiple places in the resonant cavity 100. Specifically, in Example 1, the tuning circuit also includes a directional coupler 303, which is used to directionally couple the incident power signal and send it to the resonant cavity 100.

[0063] Example 2, please refer to Figure 1, further improved on the basis of Example 1, the tuning circuit 300 also includes a first bandpass filter 304 and a second bandpass filter 305; the functional parameters of the first bandpass filter 304 and the second bandpass filter 305 are the same; the first bandpass filter 304 is used to receive the incident power signal output from the directional coupler 303; the second bandpass filter 305 is used to receive the resonant cavity 100 reflected power signal from the resonant cavity 100; the signal output ends of the first bandpass filter 304 and the second bandpass filter 305 are simultaneously connected to the signal input ends of the amplitude and phase detection circuit 306. The two inputs of the amplitude detection and phase detection circuit 306 are respectively derived from the incident power signal output by the directional coupler 303 and the resonant cavity 100 reflected power signal of the resonant cavity 100, and these two signals are filtered by the same bandpass filter before being input into the amplitude detection and phase detection circuit 306; on the one hand, the second bandpass filter 305 can filter out the spurious signals generated by the secondary electrons or other factors in the Pick-up signal, so that the amplitude detection and phase detection circuit 306 can work stably; on the other hand, since the second bandpass filter 305 itself will produce a phase delay on the input signal, and the phase delay effect on signals of different frequencies in the working frequency band is different, the first bandpass filter 304 is added, and the functional parameters of the two bandpass filters are made the same, which can eliminate the phase delay error caused by a single filter when the cyclotron works at different frequencies (considering that the frequency of the signal source 301 is consistent with the frequency of the cyclotron accelerator).

[0064] Example 3, please refer to Figure 1 , further improved on the basis of Example 2, the tuning circuit 300 also includes an ADC circuit 308 and a PLC310; the signal input end of the ADC circuit 308 is connected to the signal output end of the sample and hold 307, and the signal output end of the ADC circuit 308 is connected to the signal input end of the PLC310; the signal output end of the PLC310 is used to connect to the tuning device 200; the ADC circuit 308 is used to receive the phase difference signal output by the amplitude and phase detection circuit 306, and convert it into a digital signal and send it to the PLC310 for storage; the PLC310 is used to store and calculate the phase difference change value within the same preset interval time, and convert it to obtain the corresponding change value of the resonant cavity 100 frequency, and control the tuning device 200 to perform the frequency adjustment action according to the corresponding change value of the resonant cavity 100 frequency.

[0065] Example 5, please refer to Figure 1 In any one of embodiments 1 to 4, the signal source 301 is a radio frequency signal source 301, which can transmit a pulse wave signal or a continuous wave signal.

[0066] Example 6, please refer to Figure 1 For the signal source 301 that transmits the pulse wave signal, one embodiment of setting a specific moment is that the signal source 301 can output a macro-pulse modulation signal after macro-pulse modulation of the signal, and the macro-pulse modulation signal switches between a low-level state and a high-level state; when the macro-pulse modulation signal enters the low-level state, the sample holder is reset, and when the macro-pulse modulation signal enters the high-level state, according to the first time length, the end time of the first time length is used as the sampling time, and at the same time, the sample holder 307 triggers the sampling and holding of the phase difference output by the amplitude and phase detection circuit 306, and obtains the first phase difference and the second phase difference of the corresponding incident power signal and reflected power signal respectively. Specifically, a comparator 309 is further provided between the ADC circuit 308 and the PLC 310. The comparator 309 includes a positive input terminal and a negative input terminal. When the macro pulse modulation signal enters a low level state, the voltage of the negative input terminal of the comparator 309 is higher than the voltage of the positive input terminal. The comparator 309 outputs a low level to the PLC 310. The PLC 310 marks the data transmitted by the ADC circuit 308 at this time as the first data value and stores it. When the macro pulse modulation signal enters a high level state, the voltage of the positive input terminal of the comparator 309 is higher than the voltage of the recurrence input terminal. The comparator 309 outputs a high level to the PLC 310. The PLC 310 marks the data transmitted by the ADC circuit 308 at this time as the second data value and stores it. Specifically, inside the PLC 310, the first data value and the second data value corresponding to two adjacent pulse periods are recorded as a data group, and the sequence numbers j are marked in order, and j=1, 2, 3, ...

[0067] Example 7, please refer to Figure 1, for the signal source 301 that transmits a continuous wave signal, the signal with a frequency of f1 is a continuous wave signal. When the signal source outputs a continuous wave signal, the signal source is set to generate a trigger signal according to a preset period. The initial signal of the trigger signal is the moment when the first duration ends. The trigger signal is transmitted to the sample holder 307, and the moment when the sample holder 307 receives the trigger signal is used as the adoption moment. At this time, the sample holder 307 triggers the sampling and holding of the phase difference output by the amplitude and phase detection circuit 306. This solution can solve the technical problem that when the RF signal source 301 outputs a continuous wave state, the macro pulse modulation signal PWM always maintains a high level (or a low level), and it is difficult to effectively trigger the sample holder 307, resulting in the PLC310 being unable to obtain the real amplitude difference and phase difference, and the cyclotron is at risk of being out of control. To address this problem, when the signal source 301 outputs a continuous wave, a trigger signal (such as a PWM signal) with a fixed frequency (such as 1kHz) is generated to trigger the sample holder 307, so that the method can be applied to the cyclotron resonant cavity 100 operating in the continuous wave mode.

[0068] See also Figure 2 , taking the example of the signal source generating macro pulse modulation signal to explain the technical concept, before the cyclotron accelerator works, the static frequency f0 of the resonant cavity can be measured by a vector network analyzer. Figure 2 As shown, at time t1, the signal source generates a macro pulse modulation signal to modulate the initial signal of the power source. The signal source sets the output frequency to f1 (f1 = f0). The modulated initial signal is amplified by the amplifier to generate the corresponding incident power signal. The incident power signal is coupled to the resonant cavity through the directional coupler. Due to the secondary electron multiplication effect and other factors in the cavity, it is impossible to generate an ideal electric field in the cavity instantly, that is, the establishment of the "resonant electric field" requires a certain response time Δt0, that is, the first duration is Δt0. At time t2 = t1 + Δt0, the resonant cavity frequency is consistent with the signal source frequency, the resonant cavity reaches a resonant state, and an electric field is generated between the inner and outer conductors for particle acceleration. For example, in a certain 11MeV cyclotron accelerator, the value is Δt0 = 50us. Correspondingly, at time t3, when there is no incident power signal in the resonant cavity, it will also cause "oscillation" due to the energy storage in the cavity, but due to the electromagnetic loss of the resonant cavity, this part of the energy will be quickly dissipated on the surface of the resonant cavity.

[0069] In the process described above, the reflected power signal appears in a similar "fish" shape. The "fish tail", i.e. the time period from t1 to t2, is caused by the response time of the cavity, and the "fish head", i.e. after t3, is the oscillation caused by the energy storage of the cavity. The signal amplitude in the middle part of the reflected signal, i.e. the "fish belly", i.e. the time period from t2 to t3, remains unchanged, which can be regarded as the time of stable resonance of the cavity. Correspondingly, within a single macro pulse cycle, the Pick-up signal appears in a "shuttle" shape. At t2, the signal source outputs a PWM signal to the sample-and-hold device at the back end of the amplitude and phase detection circuit, and the ADC triggers sampling and completes the digital-to-analog conversion.

[0070] In Example 7, preferably, Δt>Δt0=t2-t1 is set as the first time length, which can effectively avoid the error caused by direct sampling at time t1.

[0071] Embodiment 8 is a further improvement based on the above embodiments. The amplitude and phase detection circuit 306 can output the amplitude difference between the incident power signal and the reflected power signal of the resonant cavity 100 while outputting the phase difference between the incident power signal and the reflected power signal of the resonant cavity 100. Specifically, the amplitude difference is used to determine the possibility of vacuum breakdown inside the resonant cavity 100. The amplitude difference of the two signals given by the amplitude and phase detection circuit 306 can determine the "sparking" state of the resonant cavity 100 based on the following principle: the "sparking" of the resonant cavity 100 means that vacuum breakdown occurs inside the resonant cavity 100 due to various reasons, and conduction occurs between the inner and outer conductors of the resonant cavity 100, resulting in a change in the frequency of the resonant cavity 100. The frequency of the resonant cavity 100 is not equal to the frequency of the incident power fed into the resonant cavity 100. The resonant cavity 100 cannot resonate, which will cause the amplitude of the Pick-up signal coupled from the resonant cavity 100 to change rapidly, thereby causing the amplitude difference between the Pin signal and the Pick-up signal given by the amplitude and phase detection circuit 306 to change before and after the preset interval time. According to the size of the change value of the amplitude difference, it can be used to determine the possibility of vacuum breakdown inside the resonant cavity 100 and the frequency of vacuum breakdown in the resonant cavity 100, so that the signal power amplified by the signal amplifier can be adjusted to make the cyclotron resonant cavity 100 work stably.

[0072] Embodiment 9 is a further improvement based on the above embodiments. The tuning device 200 includes a tuning capacitor rod, a capacitor plate and other devices that can be used for frequency tuning of the resonant cavity 100.

[0073] Example 10, taking the signal source 301 that transmits a pulse wave signal and the tuning rod as the tuning device 200 as an example, a method for dynamically adjusting the cyclotron resonant cavity frequency using the above circuit is described in detail, including the following steps:

[0074] A1. Before the cyclotron works, the static frequency f0 of the resonant cavity is measured; specifically, in step A1, the static frequency of the resonant cavity is measured by a vector network analyzer; in addition, a first time length Δt is set, wherein Δt0≤Δt≤t3-t2, Δt0 is the time length for the resonant cavity to reach the resonant state from the initial state, and t3-t2 is the time when the resonant cavity starts to oscillate;

[0075] A2, outputting a signal with a frequency of f1 through the signal source 301, wherein the frequency f1 matches the particle acceleration parameter in the cyclotron accelerator; and outputting it to the resonant cavity through the power amplifier and the directional coupler in sequence, wherein f1=f0, the signal with a frequency of f1 is a macro-pulse modulated signal after macro-pulse modulation, and recording the time when the resonant cavity starts to receive the incident power signal in each pulse cycle as the initial time of the corresponding pulse cycle;

[0076] A3. According to the first time length, in each pulse cycle, the moment when the resonant cavity reaches the resonant state is used as the sampling moment of the current pulse cycle, and at the sampling moment of each pulse cycle, the incident power signal and the reflected power signal are sampled simultaneously;

[0077] A4. Preset the target range of the resonant cavity frequency change;

[0078] A5. In each pulse cycle, the sampled incident power signal and reflected power signal are analyzed and converted to obtain the resonant cavity frequency change value Δf; and it is determined whether the resonant cavity frequency change value Δf is within the resonant cavity frequency change target range preset in step A4;

[0079] If the resonant cavity frequency change value Δf is within the preset resonant cavity frequency change target range, then continue to repeat steps A2 to A5;

[0080] If the resonant cavity frequency change value Δf is outside the preset resonant cavity frequency change target range, jump to step A6;

[0081] Specifically, the sampled incident power signal and reflected power signal are analyzed and converted to obtain the resonant cavity frequency change value, including the following steps:

[0082] A5.1. At the sampling time of the i-th pulse cycle, the phases of the incident power signal and the reflected power signal are collected respectively, and the phase difference ΔPhase corresponding to the i-th sampling time is obtained. i0 ;

[0083] A5.2. At the sampling time of the i+1th pulse cycle, the phases of the incident power signal and the reflected power signal are collected respectively, and the phase difference ΔPhase corresponding to the sampling time of the i+1th pulse cycle is obtained. i+1 ;

[0084] A5.3. ΔPhase obtained according to steps A5.1 and A5.2 i0 and ΔPhase i+1 , calculate the jth phase difference change value delta j =ΔPhase i+1 -ΔPhase i0 , {i,j=1,2,3,...}, ΔPhase i0 , ΔPhase i+1 are the phase differences corresponding to the i-th pulse period and the i+1-th pulse period respectively;

[0085] A5.4. According to the phase difference change value delta obtained in step A5.3 j , and the corresponding resonant cavity frequency change value Δf is obtained by conversion j , where the jth delta j The corresponding resonant cavity frequency change Δf j The conversion relationship between them is: delta j = kΔf j ; Where k is a non-zero constant;

[0086] A6, according to the resonant cavity frequency change value Δf j , adjust the resonant cavity frequency, and return to execute steps A1 to A5 to achieve dynamic adjustment of the cyclotron resonant cavity frequency.

[0087] In steps A5.1 and A5.2, the incident power signal and the reflected power signal pass through the first bandpass filter 304 and the second bandpass filter 305 respectively and enter the amplitude and phase detection circuit 306, and the amplitude and phase detection circuit 306 compares the phases of the two.

[0088] In step A5.1, the phase difference ΔPhase i0 The data is transmitted to the sample and hold device 307 for sampling and holding and transmitted to the ADC circuit 308 for conversion from analog signal to digital signal, and then transmitted to the comparator 309. The comparator 309 determines and outputs a low level to the PLC 310. The PLC 310 marks the data transmitted by the ADC circuit 308 as the first data value and stores it;

[0089] In step A5.2, the obtained phase difference ΔPhase i+1The data is transmitted to the sample and hold device 307 for sampling and holding and transmitted to the ADC circuit 308 for conversion from analog signal to digital signal, and then transmitted to the comparator 309. The comparator 309 determines and outputs a high level to the PLC 310. The PLC 310 marks the data transmitted by the ADC circuit 308 at this time as the second data value and stores it.

[0090] In step A5.3, the PLC calculates the jth phase difference change value delta j =ΔPhase i+1 -ΔPhase i0 ,

[0091] {i,j=1,2,3,...}.

[0092] In step A6, return to execute step A1 to step A5 to re-obtain the first time length to ensure that when sampling the reflected power signal, the sampling time is located in the stable period of the reflected power signal to ensure the sampling accuracy of the reflected power signal.

[0093] In summary, the method and tuning circuit for dynamically adjusting the cyclotron resonant cavity frequency disclosed in the present invention have the following technical effects:

[0094] 1. The present invention adopts a method of dynamically comparing the phase difference between the incident power signal and the reflected power signal, and converts the resonant cavity frequency change value according to the conversion relationship between the phase difference change value and the frequency change value, thereby compensating for the cyclotron resonant cavity frequency drift, thereby ensuring that the cyclotron accelerator can always maintain a stable working state under conditions such as changes in the resonant cavity caused by temperature and adjustment of the ion source position.

[0095] 2. The present invention uses the macro-pulse modulation signal of the radio frequency signal source to trigger the sampling and holding circuit, which can compensate for the frequency drift of the cyclotron resonant cavity under different macro-pulse frequencies and different duty cycles, and can be applied to the cyclotron resonant cavity working in the continuous wave mode.

[0096] 3. The present invention eliminates the risk of operational errors caused by manually adjusting the tuning device based on experience, and enhances the technical interoperability between different cyclotrons.

[0097] 4. The amplitude and phase detection circuit of the present invention can output the phase difference between the incident power signal and the reflected power signal, and at the same time can output the amplitude difference between the incident power signal and the reflected power signal, which can be used to judge the degree of "mismatch" of the resonant cavity and the frequency of "sparking", thereby integrating multiple functions into one control circuit and reducing the control cost of the cyclotron resonant cavity.

[0098] 5. The present invention dynamically adjusts the frequency of the resonant cavity so that the frequency of the power source, the frequency of the resonant cavity, and the frequency of the magnetic field are always consistent and consistent with the physical design of the accelerator, which can effectively ensure the intensity and quality of the extracted beam of the cyclotron accelerator, and can effectively solve the problem of "the orbit of the bunch deviates from the design value and bombards the vacuum box and other devices, causing the activation level of the accelerator to rise, making the operation and maintenance of the accelerator difficult."

[0099] It is understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. Under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. The embodiments described in the present invention are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein may be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all other embodiments obtained by ordinary technicians in the art without creative work based on the embodiments in the present invention belong to the scope of protection of the present invention.

Claims

1. A method for dynamically adjusting the frequency of a cyclotron resonant cavity, characterized in that: The following steps are involved: S1, obtaining a first time length, wherein the first time length is greater than or equal to the time length required for the resonant cavity to reach a resonant state from an initial state; S2, feeding an incident power signal into the resonant cavity, wherein the incident power signal matches the particle acceleration parameter in the cyclotron, and the time when the resonant cavity starts to receive the incident power signal is recorded as the initial time; S3, according to the first duration, taking the end time of the first duration as the sampling time, and sampling the incident power signal and the reflected power signal at the same time at the sampling time; S4, preset the target range of the resonant cavity frequency change; S5, analyzing the sampled incident power signal and reflected power signal and converting them to obtain the resonant cavity frequency change value Δf; and determining whether the resonant cavity frequency change value Δf is within the resonant cavity frequency change target range preset in step S4; If the resonant cavity frequency change value Δf is within the preset resonant cavity frequency change target range, then continue to repeat steps S2 to S5; If the resonant cavity frequency change value Δf is outside the preset resonant cavity frequency change target range, the process jumps to step S6; S6. Adjust the resonant cavity frequency according to the resonant cavity frequency change value Δf, and return to execute steps S1 to S5 to achieve dynamic adjustment of the cyclotron resonant cavity frequency.

2. The method for dynamically adjusting the cyclotron cavity frequency according to claim 1, characterized in that: In step S1, obtaining a first duration includes the following steps: S1.1, feeding an incident power signal into the resonant cavity, wherein the incident power signal matches the particle acceleration parameter in the cyclotron, and the time when the resonant cavity starts to receive the incident power signal is recorded as the initial time; S1.2, performing waveform detection on the reflected power signal of the resonant cavity; S1.3, according to the reflected power signal waveform of the resonant cavity, the moment when the reflected power signal waveform enters a stable state is taken as the moment when the resonant cavity enters a resonant state; S1.

4. Subtract the time when the resonant cavity enters the resonant state from the initial time to obtain the time required for the resonant cavity to reach the resonant state from the initial state, and set the first time to be greater than or equal to the time required for the resonant cavity to reach the resonant state from the initial state.

3. The method for dynamically adjusting the cyclotron cavity frequency according to claim 1, characterized in that: In step S2, the incident power signal is obtained by amplifying the power of a signal source outputting a signal with a frequency of f1; the frequency f1 matches the particle acceleration parameter in the cyclotron; wherein f1=f0, f0 is the static frequency of the resonant cavity; The signal with the frequency f1 is a pulse signal or a continuous signal.

4. The method for dynamically adjusting the cyclotron cavity frequency according to claim 3, characterized in that: The signal with a frequency of f1 is a pulse signal, and correspondingly, the resonant cavity has a first moment t1, a second moment t2 and a third moment t3 in each pulse cycle; at the second moment t2, the resonant cavity reaches a resonant state, and at the third moment t3, the resonant cavity enters an oscillating state; the first time length is set to be greater than or equal to t2-t1 and less than or equal to t3-t2; In step S5, the sampled incident power signal and reflected power signal are analyzed and converted to obtain a resonant cavity frequency change value, including the following steps: S5.

1. At a sampling time corresponding to the first pulse signal, the phases of the incident power signal and the reflected power signal are respectively collected, and a first phase difference ΔPhase0 is obtained; S5.2, at a sampling time corresponding to a second pulse signal, respectively collecting the phases of the incident power signal and the reflected power signal, and obtaining a second phase difference ΔPhase′; the second pulse signal is the next pulse signal adjacent to the first pulse signal; S5.3, according to the first phase difference ΔPhase0 and the second phase difference ΔPhase′ obtained in steps S5.2 and S5.3, calculate the phase difference change value delta=ΔPhase′-ΔPhase0; S5.

4. According to the phase difference change value delta obtained in step S5.3, the corresponding resonant cavity frequency change value Δf is converted.

5. The method for dynamically adjusting the cyclotron cavity frequency according to claim 1, characterized in that: In step S6, the frequency of the resonant cavity is adjusted by using a tuning rod inserted into the resonant cavity. Before executing step S6, the relationship between the length change value ΔL of the tuning rod inserted into the resonant cavity and the change value Δf of the resonant cavity frequency is first obtained. In step S6, according to the change value Δf of the resonant cavity frequency, the corresponding change value ΔL of the length of the tuning rod inserted into the resonant cavity is obtained, and then the length of the tuning rod inserted into the resonant cavity is adjusted to adjust the resonant cavity frequency.

6. The method for dynamically adjusting the cyclotron cavity frequency according to claim 4, characterized in that: In step S2, the signal source is a radio frequency signal source, the signal with a frequency of f1 is a macro-pulse modulated signal after macro-pulse modulation, and the macro-pulse modulated signal switches between a low level state and a high level state; when executing step S5, the macro-pulse modulated signal is in a high level state.

7. The method for dynamically adjusting the cyclotron cavity frequency according to claim 3, characterized in that: In step S2, the signal source is a radio frequency signal source, the signal with a frequency of f1 is a continuous wave signal, and while the signal source outputs a continuous wave signal, the signal source is also set to generate a trigger signal according to a preset period, and the initial signal of the trigger signal is the moment when the first duration ends.

8. A tuning circuit for dynamically adjusting the frequency of a cyclotron resonant cavity, used to implement the method for dynamically adjusting the frequency of a cyclotron resonant cavity as claimed in claim 4, characterized in that: include: A signal source, used for outputting a pulse signal with a frequency of f1; A power amplifier is used to amplify the signal with a frequency of f1 output by the signal source to obtain an incident power signal; An amplitude and phase detection circuit, used for receiving an incident power signal and a reflected power signal respectively, and outputting a phase difference between the incident power signal and the reflected power signal; The sampler and holder is used to sample and hold the phase difference output by the amplitude and phase detection circuit at a non-sampling time, and the signal output end of the amplitude and phase detection circuit is connected to the signal input end of the sampler and holder.

9. The tuning circuit for dynamically adjusting the cyclotron cavity frequency according to claim 8, characterized in that: The tuning circuit further comprises a first bandpass filter and a second bandpass filter; the first bandpass filter and the second bandpass filter have the same functional parameters; The first bandpass filter is used to receive the incident power signal output from the directional coupler; The second bandpass filter is used to receive a reflected power signal from the resonant cavity; The signal output ends of the first band-pass filter and the second band-pass filter are simultaneously connected to the signal input end of the amplitude and phase detection circuit.

10. The tuning circuit for dynamically adjusting the cyclotron cavity frequency according to claim 9, characterized in that: The tuning circuit further comprises an ADC circuit and a PLC; the signal input end of the ADC circuit is connected to the signal output end of the sample and holder, the signal output end of the ADC circuit is connected to the signal input end of the PLC; the signal output end of the PLC is used to connect to the tuning device; The ADC circuit is used to receive the phase difference signal output by the amplitude and phase detection circuit, and convert it into a digital signal and send it to the PLC for storage; The PLC is used to store and calculate the phase difference change value within the same preset interval time, and convert it to obtain the corresponding resonant cavity frequency change value, and control the tuning device to perform frequency adjustment action according to the resonant cavity frequency change value.

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